Synergistic effect of guanidinium tetrafluoroborate boosting photovoltaic performance of perovskite solar cells

The power conversion efficiency (PCE) of the perovskite solar cell (PSC) has made an illustrious breakthrough in the past ten years. However, it is still a great challenge to fabricate high-quality perovskite films due to the intrinsic high defect-density and internal non-radiative recombination, which has severely hindered the development of PSCs. Herein, a new-type additive guanidinium tetrafluoroborate (GuaBF(4)) is introduced to improve the perovskite films quality, thus boosting photovoltaic performance of resultant PSCs. It is demonstrated that owing to the synergistic effect of Gua(+) and BF4-, the introduction of GuaBF(4) can improve the quality of CH3NH3PbI3 (MAPbI(3)) films. Through optimizing the concentration of GuaBF(4), the MAPbI(3) film with GuaBF(4) displays higher crystallinity, enlarged crystal grain and smoother surface. Furthermore, by virtue of the strong interaction between MAPbI(3) and GuaBF(4), the inclusion of GuaBF(4) can effectively passivate traps/defects in perovskite films, thereby diminishing the non-radiative recombination and promoting the charge carrier transportation. Consequently, a high-performance MAPbI(3) PSC with a PCE of 20.62 %, lessened hysteresis behavior and improved moisture stability is achieved. Our research emphasizes on the significance of the synergistic effect in additives for high-performance PSCs.